Light-emitting device and display device

ABSTRACT

Although an organic resin substrate is highly effective at reducing the weight and improving the shock resistance of a display device, it is required to improve the moisture resistance of the organic resin substrate for the sake of maintaining the reliability of an EL element. Hard carbon films are formed to cover a surface of the organic resin substrate and outer surfaces of a seating member. Typically, DLC (Diamond like Carbon) films are used as the carbon films. The DLC films have a construction where carbon atoms are bonded into an SP 3  bond in terms of a short-distance order, although the films have an amorphous construction from a macroscopic viewpoint. The DLC films contain 95 to 70 atomic % carbon and 5 to 30 atomic % hydrogen, so that the DLC films are very hard and minute and have a superior gas barrier property and insulation performance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device (hereinafter referred to as alight-emitting device) that has an element (hereinafter referred to as alight-emitting element) where a thin film including a luminescentmaterial is sandwiched between a pair of an anode electrode and acathode electrode. In particular, the present invention relates to alight-emitting device whose light-emitting element includes a thin film(hereinafter referred to as a light-emitting layer) made of anelectro-luminescent material (EL material). The present invention alsorelates to a display device that uses a substrate made of an organicresin material and, more particularly, to a display device where a pixelportion is formed on such a substrate using thin-film transistors and anEL material.

2. Description of the Related Art

Liquid crystal panels or EL materials applied to display devices maycontribute to reduction in weight and thickness thereof in comparisonwith conventional CRTs. Therefore, attempts have been recently made toapply display devices using the liquid crystal panels or EL materials tovarious fields. Also, it has now become possible to connect portabletelephones and personal digital assistants (PDAs) to the Internet, whichleads to the dramatic increase in the amount of image information to bedisplayed thereon and creates increasing demand for high-definitioncolor display devices.

Display devices used for such portable information terminals need to bereduced in weight and, for instance, portable telephones whose weightsare below 70 g are now on the market. For the reduction in weight,almost all components, such as electronic components, housing, andbatteries, of the portable information terminals are subjected toreengineering. For the further weight reduction, however, displaydevices need to be reduced in weight.

Display devices are produced using glass substrates in many cases, sothat one conceivable method for weight reduction would be to reduce thethickness of the glass substrates. In this case, however, the glasssubstrates tend to be cracked and the shock resistance thereof islowered. This becomes a serious hindrance to the application of displaydevices including such thin class substrates to portable informationterminals. To meet demand for weight reduction as well as shockresistance, the development of display devices using organic resinsubstrates (plastic substrates) is under consideration.

For instance, light-emitting devices that have light-emitting elementsproduced using EL materials are currently under development. Displaydevices whose pixel portions are formed using light-emitting elementsare capable of emitting light by themselves and further do not requirelight sources, such as backlights, unlike liquid crystal displaydevices. As a result, such light-emitting elements are highly expectedas an effective means for reducing weights as well as thickness ofdisplay devices.

The construction of a typical light-emitting element using an organic ELmaterial is shown in FIG. 22. In this drawing, an insulator 2201, ananode 2202, a light-emitting layer 2203, and a cathode 2204 arelaminated to form a light-emitting element 2200.

Before being observed by an observer 2206, light 2205 emitted from thelight-emitting layer directly passes through the anode 2202, or isreflected by the cathode 2204 and then passes through the anode 2202.That is, the observer 2206 observes the light 2205 that and passesthrough the anode 2202 to be emitted in picture elements where thelight-emitting layer 2203 performs light emission.

A light-emitting element is composed of two electrodes: an anode thatinjects holes into an organic compound layer including a light-emittinglayer, and a cathode that injects electrons into the organic compoundlayer. The light-emitting element having this construction utilizes aphenomenon where light is emitted when the holes injected from the anodeare recombined with the electrons injected from the cathode within thelight-emitting layer. The organic compound layer including thelight-emitting layer is degraded by various factors, such as heat,light, moisture, and oxygen. To prevent this degradation, an ordinaryactive matrix type light-emitting device is produced by forminglight-emitting elements in a pixel portion after wiring andsemiconductor elements are formed therein.

After the formation of the light-emitting element, a first substrate, onwhich the light-emitting element have been formed, and a secondsubstrate for covering the light-emitting elements are laminated andsealed (packaged) using a sealing member. This construction prevents thelight-emitting elements from being exposed to the outside air.

It should be noted here that in this specification, all layers providedbetween a cathode and an anode are collectively referred to as anorganic compound layer. The organic compound layer has a well-knownstructure where, for instance, a hole injecting layer, a light-emittinglayer, an electron transporting layer, and an electron injecting layerare laminated with each other. A predetermined voltage is applied to theorganic compound layer by a pair of electrodes to cause therecombination of carriers, thereby causing light emission in thelight-emitting layer.

The light-emitting element, however, has a problem as to durability and,in particular, to oxidation resistance. The cathode that injectselectrons into the organic compound layer is ordinarily made of analkaline metal or an alkaline earth metal having a low work function. Itis well known that these metals tend to react with and water, therebyhaving low oxidation resistance. The oxidation of the cathode means thatthe material of the cathode loses electrons and is coated with anoxidation layer. The reduction in the number of electrons to be injectedand the oxidation coat may reduce the amount of emitted light inbrightness.

As described above, the electrode of the light-emitting element iseasily oxidized with a considerably small amount of oxygen or moistureand therefore the light-emitting element is easily degraded. Varioustechniques have been developed to prevent the oxidation of thelight-emitting element. For instance, the light-emitting element issealed with a metal or glass that is impermeable to oxygen and moisture.Also, the light-emitting element is produced to have a resin laminationconstruction or is filled with nitrogen or an inert gas. Even if thelight-emitting element is sealed with a metal or a resin, however,oxygen easily passes through small gaps and oxidizes the cathode andlight-emitting layer. Also, moisture easily passes through the resinused to seal the light-emitting element in terms of the light-emittingelement. This causes a problem in that areas (called dark spots) that donot emit light appear on a display screen and expand with the lapse oftime, which makes the light-emitting element incapable of emittinglight.

EL materials are capable of emitting blue light and thus it is possibleto realize a full-color display device of a self-light emitting typewith the materials. However, it is confirmed that organic light-emittingelements are degraded in various ways. This degradation prevents theactual use of the EL materials and a solution to this problem isurgently required. The dark spots are spot-shaped defects that do notemit light in the pixel portion and so degrade display quality. The darkspots are also defects that get worse over time. Even if thelight-emitting element is not brought into operation, the number of thedark spots is increased by the existence of moisture. It is thought thatthe cause of the dark spots is the oxidation reaction of the cathodemade of an alkaline metal. To prevent the occurrence of dark spots, asealed space is filled with dryer gas or provided with a dryer agents inwhich the light-emitting element is placed.

Also, the light-emitting element is vulnerable to heat that promotesoxidation. This means that there are many factors causing oxidation andtherefore it is difficult to make actual use of light-emitting devices.In view of the problems described above, the object of the presentinvention is to provide a light-emitting device with a high degree ofreliability and an electronic device where a high-reliability displayunit is achieved using such a light-emitting device.

It is well known that a substrate made of an organic resin material hashigh permeability to moisture, in comparison with a glass substrate. Forinstance, the permeability to moisture of polyether imide is 36.3g/m²·24 hr, that of polyimide is 32.7 g/m²·24 hr, and that of polyetherterephthalate (PET) is 12.1 g/m²·24 hr.

As is apparent from this, if a display device produced with alight-emitting element including an organic resin substrate is leftstanding in the air for a long time period, moisture gradually permeatesand the organic light-emitting element is degraded. In addition, asealing member used to seal a light-emitting element is also made of anorganic resin material, so that it is difficult to completely preventoxygen and moisture in the air from entering through sealed portions.

Also, an organic resin substrate is soft, in comparison with a metalsubstrate or a glass substrate, so that scratches or the like are easilymade thereon. Further, the long-term exposure to the direct sunlightcauses a light chemical reaction and alters the quality and color of theorganic resin substrate.

As described above, the organic resin substrate is a highly effectivemeans to realize a display device reduced in weight with high shockresistance, although there remain many problems that must be solved inorder to ensure the reliability of the light-emitting element. In viewof these problems, the object of the present invention is to provide adisplay device that uses a light-emitting element with a high degree ofreliability.

Also, if the outside light (the light existing outside thelight-emitting device) enters picture elements that do not emit light,the light is reflected by the back surface (the surface contacting theorganic compound layer) of the cathode, so that the cathode back surfacefunctions as a mirror and reflects the outside scenes. To solve thisproblem, a circular polarizing film has conventionally been applied to alight-emitting device to prevent the reflection of the outside scenestoward the observer, although this construction raises the fabricationcost because the circular polarizing film is high-priced. In view ofthis problem, the object of the present invention is to prevent thismirror reflection phenomenon of a light-emitting device without using acircular polarizing film.

SUMMARY OF THE INVENTION

According to the present invention, in a display device using an organicresin substrate, a hard carbon film is formed on a surface of thesubstrate as a protecting film that prevents from entering moisture orthe like and the scratches on the surface. In particular, a DLC (Diamondlike Carbon) film is used with the present invention. The DLC film has aconstruction where carbon atoms are bonded into a diamond bond (SP³bond) in terms of a short-distance order although the film has anamorphous construction containing a graphite bond (SP² bond) from amacroscopic viewpoint. The DLC film contains 95 to 70 atomic % carbonand 5 to 30) atomic % hydrogen, so that the DLC film is very hard andexcels in insulation. The DLC film is also characterized by low gaspermeability to moisture and oxygen. Further, it is known that thehardness of the DLC film is 15 to 25 Gpa in the case of measurementusing a micro-hardness meter.

The DLC film is formed using a plasma CVD method, a microwave CADmethod, an electron cyclotron resonance (ECR) CVD method, or asputtering method. With any of these methods, the DLC film is formed inintimate contact without heating the organic resin substrate. The DLCfilm is formed under a situation where the substrate is set on acathode. Alternatively, the DLC film is formed by applying a negativebias and utilizing ion bombardment to some extent. In the latter case,the DLC film becomes minute and hard.

The reaction gas used to form the DLC film is hydrocarbon gas, such asCH₄, C₂H₂, and C₆H₆. The DLC film is formed by ionizing the reaction gasby means of glow discharge and bombarding a cathode, to which a negativeself-bias is applied, with accelerated ions. In this manner, the DLCfilm becomes minute and flat. The DLC film may be formed without heatingthe substrate to a high temperature, so that the formation of the DLCfilm can be performed in the final manufacturing step where a displaydevice is finished.

By forming the DLC film on at least one surface of the organic resinsubstrate, the gas barrier property is improved. Alternatively, the gasbarrier property is improved by forming the DLC film on the outersurface of a sealing member used to laminate an organic resin substrate(hereinafter, an element substrate), on which TFTs and light-emittingelements are formed, with a sealing substrate for sealing thelight-emitting elements. In this case, the thickness of the DLC film isin a range of 5 nm to 500 nm. Also, by forming the DLC film on a lightincident surface, ultraviolet rays are blocked, the light chemicalreaction of the organic resin substrate is suppressed, and thedegradation of the organic resin substrate is prevented.

The DLC film that prevents oxygen and moisture from entering is formedto successively cover exposed portions of the sealing member and sideportions of the first and second substrates that are laminated toproduce the light-emitting device. The exposed portions of the sealingmember and the side portions of the first and second substrates arehereinafter collectively referred to as “end surfaces”. With aconventional technique, oxygen and moisture pass through a resinprovided at end portions. The construction described above, however,prevents moisture from entering through between the first and secondsubstrates.

A dryer agent is provided in a space between the element substrate andthe sealing substrate sealed by the sealing member, thereby suppressingthe degradation of the light-emitting elements. For instance, a bariumoxide can be used as the dryer agent. The dryer agent is provided atpositions (for instance, on a driving circuit, on a partition wall, orwithin the partition wall) outside light-emitting areas. With thisconstruction, the dryer agent absorbs gas and moisture contained in thelight-emitting elements as well as oxygen and moisture passing through asealing resin in the end portions. As a result, the degradation of thelight-emitting elements is prevented. Further, by forming an organicinterlayer insulating film using a black resin, the mirror reflectionphenomenon (the reflection of the outside scenes) of the light-emittingdevice is prevented. Also, the black resin may be used in an area inwhich the sealing member is formed.

The DLC film described above is applicable to passive type displaydevices as well as active matrix type display devices.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1D each show a position where DLC film is formed on anorganic resin substrate according to the present invention;

FIG. 2 shows the construction of a plasma CVD apparatus used to form DLCfilms used in the present invention;

FIGS. 3A and 3B each show the construction of the reaction chamber ofthe plasma CVD apparatus;

FIG. 4 is a cross to sectional view showing the constructions of thedriving circuit and pixel portion of a display device;

FIGS. 5A and 5B are respectively a top view and an equivalent circuitdiagram showing the construction of the pixel portion of the displaydevice;

FIG. 6 is a perspective view showing the external appearance of an ELdisplay device of the present invention;

FIG. 7 shows the construction of an input terminal of the displaydevice;

FIG. 8 shows the construction of the input terminal of the displaydevice;

FIGS. 9A to 9C each show an example where a dryer agent is provided inthe pixel portion;

FIG. 10 is a cross-sectional view showing the constructions of thedriving circuit and the pixel portion of the display device;

FIG. 11 is a system block diagram of an electronic device in which thedisplay device is built;

FIGS. 12A to 12E each show an example of the electronic device;

FIGS. 13A to 13D each show an example of the electronic device;

FIGS. 14A and 14B each show an embodiment mode of the present invention;

FIGS. 15A and 15B each show a CVD apparatus of the present invention;

FIGS. 16A to 16C each show an example of the embodiment mode of thepresent invention;

FIGS. 17A and 17B each show an example of the embodiment mode of thepresent invention;

FIGS. 18A to 18D each show an example of the embodiment mode of thepresent invention;

FIGS. 19A and 19B each show an example of the embodiment mode of thepresent invention;

FIGS. 20A and 20B each show an example of the embodiment mode of thepresent invention;

FIGS. 21A to 21C each show an example of the electronic device that usesa light-emitting device as its display unit;

FIG. 22 shows an example of the conventional technique; and

FIGS. 23A to 23E each show an example of the embodiment mode of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment modes and embodiments of the present invention are describedin detail below with reference to the drawings.

Embodiment Mode 1

Embodiment Mode 1 is described below with reference to FIGS. 1A to 1Deach showing a display device using a light-emitting element. FIG. 1Ashows a state where an element substrate 101, on which a driving circuit108 and a pixel portion 109 are formed using TFTs (thin-filmtransistors) and a sealing substrate 102 are fixed using a sealingmember 105. A light-emitting element 103 is formed in the sealed spaceformed between the element substrate 101 and the sealing substrate 102.A dryer agent 106 is provided on the driving circuit or in the vicinityof the sealing member 105. It should be noted here that although notshown in this drawing, the dryer agent 106 may be contained in apartition wall 110 that is formed across the pixel portion 109 and thedriving circuit 108.

Each of the element substrate and sealing substrate is made of anorganic resin material, such as polyimide, polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polyether sulfone (PES), oraramid. The thickness of each of these substrates is set at around 30 to120 μm to maintain the flexibilities of the substrates.

In the example shown in FIG. 1A, DLC films 107 are formed at endportions as gas barrier layers. Note that the DLC films are not formedon an external input terminal 104. An epoxy adhesive is used as thesealing member. To prevent from entering moisture, the DLC films 107 areformed to cover the sealing member 105 and the end portions of theelement substrate 101 and the seating substrate 102.

FIG. 1B shows a construction where a DLC film 110 is formed to cover theundersurface of the element substrate 101, in addition to the DLC films107 formed to cover the sealing member 105 and the end portions of thesubstrates 101 and 102. Although depending on the thickness, a DLC filmhas low permeability to light whose wavelength is short (500 nm orless). Therefore, in this example, no DLC film is formed on the displaysurface (the main surface on a display side) of the sealing substrate102. This construction, however, completely prevents moisture fromentering the element substrate 101 on which the TFTs are formed. As aresult, the degradation of the TFTs and the light-emitting element doesnot occur.

FIG. 1C shows a construction where gas barrier property is improved. Inthis drawing, a DLC film is formed to cover whole surfaces of theelement substrate 101, the sealing substrate 102, and the sealing member105, except for the external input terminal 104. In addition to theimprovement in gas barrier property, this construction has the effect ofpreventing scratches or the like on the surfaces because the surfaces ofthe plates are protected by the DLC film.

FIG. 1D shows an example where DLC films are formed on the elementsubstrate 113 and the sealing substrate 114 beforehand. Then, other DLCfilms are additionally formed to cover the end portions in which thesealing member for fixing these plates is formed.

FIG. 2 shows an example of a CVD apparatus used to form DLC films. Thisdrawing mainly shows a vacuum chamber and other related processingmeans. As shown in this drawing, the vacuum chamber includes a commonchamber 202 that has a transporting means for transporting a targetsubstrate 218 to be processed, a load lock chamber 201 that inserts andremoves the target substrate, and a first reaction chamber 203 and asecond reaction chamber 204 that form DLC films on the target substrate.The load lock chamber 210 and the first and second reaction chambers 203and 204 are connected to the common chamber 202 via gate valves 205 to207. Also, these chambers 201 to 204 are provided with exhausting means208, 209, 211, and 214.

The first reaction chamber 203 is provided with a gas introducing means212 and a discharge causing means 213. Similarly, the second reactionchamber 204 is provided with a gas introducing means 215 and a dischargecausing means 216. These gas introducing means introduce above-describedhydrocarbon gas or Ar, H₂ and the like into the chambers. Each dischargecausing means is composed of a cathode and an anode, which are arrangedin respective reaction chambers, and a high-frequency (1 to 120 MHz)power source. DLC films are formed by setting the target substrate onthe cathode side in the reaction chamber. Therefore, if DLC films are tobe formed on both of the element substrate and the sealing substrate, asshown in FIG. 1C, the posture of the target substrate need to be chanced(for instance, the target substrate is required to be turned around).

FIGS. 3A and 3B each show a state where a DLC film is formed on onesurface of the target substrate in the first reaction chamber 203 andanother DLC film is formed on the other surface of the target substratein the second reaction chamber 204.

In FIG. 3A, a reaction chamber 301 is connected to a gas introducingmeans 302 and includes a cathode 305, to which a high-frequency powersource 304 is connected, and an anode 306 having a shower plate 309 forsupplying gas to the reaction chamber. The reaction chamber 301 is alsoconnected to an exhausting means 303. A target substrate 308 is placedon the cathode 305. Pressure pins 307 are used to transport the targetsubstrate. With this construction, a DLC film is formed on one-surfaceand end portions of the target substrate in the reaction chamber. Also,if the cathode has a stepped cross section, as shown in FIG. 3A, itbecomes possible to have the formed DLC film also cover undersurfaceareas in the vicinity of the end portions of the target substrate.Needless to say, the DLC film covering the undersurface areas is thinnerthan that covering other areas.

FIG. 3B shows a example of construction of a reaction chamber where aDLC film is formed on a surface opposing to that processed in FIG. 3A(the undersurface of the target substrate). A reaction chamber 310 isconnected to a gas introducing means 312 and includes a cathode 315, towhich a high-frequency power source 314 is connected, and an anode 316having a shower plate 320 for supplying gas to the reaction chamber 310.The reaction chamber 310 is also connected to an exhausting means 313. Atarget substrate 318 is required to be set at the cathode 315, so thatthe reaction chamber 310 is further provided with a holder 319 and amechanism 311 for moving the holder up or down. The target substrate 318is first held by pressure pins 317 and then is set at the cathode 315 bythe holder 319 that is elevated by the mechanism 311. In this manner, aDLC film is formed on the surface opposing to that processed in FIG. 3A(the undersurface of the target substrate).

As described above, with the plasma CVD apparatus shown in FIGS. 2, 3A,and 3B, it becomes possible to realize the display devices shown inFIGS. 1A to 1D where DLC films are formed as gas barrier layers.Needless to say, FIGS. 2, 3A, and 3B each show an example constructionof the CVD apparatus, so that the display devices shown in FIGS. 1A to1D may be produced with a film forming apparatus having anotherconstruction. For instance, DLC films may be formed with a CVD apparatusthat utilizes a microwave or electron cyclotron resonance.

The DLC films used as gas barrier layers more effectively preventmoisture and oxygen from entering a sealed space and thus enhances thestability of a light-emitting element. For instance, this constructionreduces the number of dark spots resulting from the oxidation of acathode.

Embodiment Mode 2

FIGS. 14A and 14B each show an example where a pixel portion and adriving circuit are formed on a substrate having an insulating surface(such as a glass substrate, a ceramic substrate, a crystallized glasssubstrate, a metal substrate, or a plastic substrate).

In these drawings, reference numeral 1401 represents a gate-side drivingcircuit; numeral 1402, a source-side (data-side) driving circuit; andnumeral 1403, a pixel portion. Signals transmitted to the gate-sidedriving circuit 1401 and the source-side driving circuit 1402 aresupplied from an FPC (flexible print circuit) 1405 via input wiring1404.

A sealing substrate 1406 is used to seal light-emitting elements. Thelight-emitting elements emit light toward the sealing substrate 1406, sothat the sealing substrate 1406 is required to have transparency.Numeral 1407 represents a sealing resin used to seal the sealingsubstrate 1406 and the element substrate 1400. A cross-sectional viewtaken along the line A-A′ in FIG. 14A is shown in FIG. 14B. In thisdrawing, the sealing substrate 1406 is also covered with a DLC film toprevent the penetration of oxygen.

After an insulating film 1411 is formed on the element substrate 1400, alight-emitting element 1412 composed of a cathode 1413, an organiccompound layer (including a light-emitting layer) 1414, and an anode1415 is formed on the insulating film 1411. A protecting layer 1417 isfurther formed on the cathode 1413 to protect the light-emitting element1412 that is easily oxidized by oxygen and moisture. It is preferablethat the insulating film is transparent or translucent to visibleradiation.

The cathode 1413 and the anode 1415 are also transparent or translucentto visible radiation. Here, transparency to visible radiation means thatthe permeability to visible radiation is around 80 to 100% andtranslucency to visible radiation means that the permeability to visibleradiation is around 50 to 80%. The anode 1415 and the cathode 1413 mustbe respectively made of a conductive oxide film with a work function of4.5 to 5.5 and a conductive film with a work function of 2.0 to 3.5(typically, a metal film including an element belonging to Group 1 or 2of the periodic table). In many cases, however, the metal coat is nottransparent to visible radiation, so that it is preferable that theconstruction shown in FIGS. 14A and 14B is used. The cathode 1413 thatis translucent to visible radiation is formed by laminating a thin metalfilm with a thickness of 5 to 70 nm (preferably, 10 to 30 nm) and aconductive oxide film (ITO, for instance). Note that the organiccompound layer (including the light-emitting layer) 1414 may adopt awell-known structure and the organic compound layer may be used alone orlaminated with a carrier (electrons or holes) injecting layer, a carriertransporting layer, or a carrier blocking layer.

To prevent the degradation of the light-emitting element due to oxygenand moisture, DLC films are formed at the end portions of the displaydevice and a dryer agent is further provided between the first substrate1400 and the second substrate 1406. Note that the dryer agent isprovided by forming a barium oxide (BaO₂) layer on the second substrateusing an EB vapor deposition method or by sealing the dryer agent in apowder state between the substrates. Alternatively, the dryer agent maybe provided to function as a spacer by mixing the dryer agent with aresin and providing the mixture on partition walls or at positions (suchas on the driving circuit or wiring that connects the driving circuit topicture elements) outside light-emitting areas. Further, the dryer agentmay be mixed with a resin that is the material of the partition walls.The dryer agent may be provided with any of the methods described above.Note that in this embodiment mode, powder of barium oxide is provided asthe dryer agent in a space 1409 between a sealing resin 1407 and a resin1408, as shown in FIG. 14B.

With the construction shown in FIGS. 14A and 14B, emitted light passesthrough the cathode and is directly observed by an observer. Most of theoutside light is absorbed by an organic interlayer insulating film 1419made of a black resin, so that the amount of the outside light reflectedtoward an observer is reduced to a level where no problem arises. As aresult, the reflected light does not reach the observer and the outsidescenes are not reflected by the surface facing the observer.

The following is a description of the method of forming DLC films at endportions of the light-emitting device produced by laminating the elementsubstrate 1400 and the sealing substrate 1406, with reference to FIGS.15A and 15B. A light-emitting device 1501 is held by a holding means1502 a in a reaction chamber 1500. The reaction chamber 1500 is providedwith an introducing opening 1508 and an exhausting opening 1509 thatrespectively introduces and exhausts gas used to form DLC films. Also,means (RF electrodes) 1503 for causing plasma are provided in thereaction chamber 1500. The holding means 1502 a is fixed to the reactionchamber and the light-emitting device 1501 on the holding means 1502 ais pressed against the holding means 1502 a by the movable holding means1502 b.

The electrodes 1503 are connected to (high-frequency) power sources 1505and matching circuits 1504. Typical RF power sources are used as thepower sources 1505. The electrodes 1503 are connected to the RF powersources 1505 that apply voltages to the electrodes 1503. A phaseadjuster 1510 is provided to adjust the phases of the RF power sources1505. With this construction, the electrodes are supplied with power,whose phases differ from each other by 180°, from the RF power sources.FIG. 15A shows a state where one pair of electrodes is provided in thereaction chamber, however, a plurality of pairs of electrodes orcylindrical electrodes may be used.

To form DLC films in end portions of the light-emitting device 1501,surfaces in the end portions need to be subjected to ion bombardment.Therefore, the holding means 1502 a is connected to a power source 1507.To generate a self-bias, a capacitor 1511 is arranged between the powersource 1507 and the holding means 1502 a. The holding means 1502 a isprovided as a means for applying a bias to the substrate. Also, theholding means 1502 b is provided to prevent the DLC films from beingformed on the entire surface of the light-emitting device 1501. That is,the holding means 1502 functions as a mask that covers a light-emittingarea and the external input terminal (FPC) to thereby prevent the DCLfilms from forming thereon. Note that the layer forming conditions areappropriately set by an operator of the film forming apparatus.

To form DLC films at end portions of the light-emitting device producedby laminating an element substrate and a sealing substrate, the holdingmeans 1502 a is divided into two masking portions: a masking portion(hereinafter, a light-emitting area mask) that covers the light-emittingarea, and a masking portion (hereinafter, an external input terminalmask) that covers the external input terminal. These masking portionsare partially connected to each other. It is preferable that the widthof the connection between the light-emitting area mask and the externalinput terminal mask is set at 5 mm or less (see FIG. 15B). It is alsopreferable that the relation between the width of the connection and theheight of the holding means 1502 b satisfies a condition“Height/Width≧around 2” (see FIG. 15B).

Aside from the holding means composed of the light-emitting area maskand the external input terminal mask, an ordinary masking tape may beused in the CVD apparatus to cover the external input terminal tothereby prevent the formation of a DLC film thereon. To prevent thedegradation of the light-emitting element due to oxygen and moisture,DLC films need to be formed in four end portions of the light-emittingdevice 1501. To effectively and evenly form the DLC films, a member 1506supporting the holding means 1502 a may be given a rotating function.

The holding means 1502 a doubles as an electrode that applies a negativeself-bias to the light-emitting device 1501. The power source 1507applies a negative self-bias to the electrode 1502. Minute DLC films areformed in the end surfaces of the light-emitting device 1501 using asource gas accelerated by the negative self-bias voltage. Note that thesource gas is an unsaturated hydrocarbon gas (such as methane, ethane,propane, or butane), an aromatic gas (such as benzene or toluene), or ahalogenated hydrocarbon where at least one hydrocarbon molecular isreplaced by a halogen element, such as F, Cl, or Br.

In the manner described above, DLC films 1510 with a thickness of 5 to100 nm (preferably, 10 to 30 nm) are formed to coat the end portions ofthe light-emitting device. FIG. 23 shows a state where DLC films areformed on a light-emitting device using the film forming apparatus ofthe present invention. DLC films are directly formed on the sidesurfaces and edge portions of the surfaces of a substrate in thisembodiment mode. However, to bring the DLC films into intimate contact,nitride films (such as silicon nitride films or silicon oxynitridefilms) may be formed as base films before the DLC films are formed. Inthis case, the thickness of the nitride films is set at 2 to 20 nm.

Embodiment 1

The present invention is applicable to various types of display devicesso long as the display devices use light-emitting elements. FIG. 4 showsan example of display device to which the present invention is applied.The display device in this drawing is an active matrix type displaydevice produced using TFTs. TFTs are classified into amorphous siliconTFTs and polysilicon TFTs, depending on what materials are used toproduce semiconductor films that form channel formation regions. Thepresent invention is applicable to both types of TFTs.

It is impossible to produce an organic resin substrate, which isresistant to heat processing at 450° C. or higher, using a commerciallyavailable material. A laser anneal technique, however, makes it possibleto produce polysilicon TFTs only by heating the substrate to 300° C. orbelow. Also, in many cases, hydrogenation processing is required to beperformed during the production of polysilicon TFTs. A plasma-aidedhydrogenation processing makes it possible to produce polysilicon TFTsonly by heating the substrate to around 200° C.

In FIG. 4, an N-channel type TFT 452 and a P-channel type TFT 453 areformed in a driving circuit portion 450, and a switching TFT 454 and acurrent control TFT 455 are formed in a pixel portion 451. These TFTsare formed using various components, such as island-like semiconductorlayers 403 to 406, a gate insulating film 407, and gate electrodes 408to 411.

A substrate 401 is made of an organic resin material (such as polyimide,polyethylene terephthalate (PET), polyethylene naphthalate (PEN),polyether sulfone (PES), or aramid) to have a thickness of 30 to 120 μm(typically, 75 μm). A blocking layer 402 is made of silicon oxynitride(SiO_(x)N_(y)) or a silicon nitride film to have a thickness of 50 to200 nm, thereby preventing the precipitation of oligomer or the likefrom the substrate 401. An interlayer insulating film includes aninorganic insulating film 418 made of silicon nitride or siliconoxynitride and an organic insulating film 419 made of acrylic orpolyimide.

The driving circuit portion 450 includes a gate-signal-side drivingcircuit and a data-signal-side driving circuit having different circuitconstructions, although the circuit constructions are not describedhere. The N-channel type TFT 452 and the P-channel type TFT 453 areconnected to wirings 412 and 413 and are used to form a shift resister,a latch circuit, and a buffer circuit.

In the pixel portion 451, data wiring 414 is connected to the source ofthe switching TFT 454 and drain-side wiring 415 is connected to the gateelectrode 411 of the current control TFT 455. Also, the source of thecurrent control TFT 455 is connected to power source wiring 417 so as toconnect a drain-side electrode 416 with the anode of the light-emittingelement. FIGS. 5A and 5B each show a top view of the pixel portionconstructed in this manner. For case of explanation, the same referencenumerals as in FIG. 4 are used in FIGS. 5A and 5B. Also, across-sectional view taken along the line A-A′ in FIG. 5A is shown inFIG. 4.

As shown in FIG. 4, partition walls 420 and 421 are formed using anorganic resin, such as acrylic or polyimide, or preferably aphotosensitive organic resin to cover the wiring. The light-emittingelement 456 is composed of an anode 422 made of ITO (indium tin oxide),an organic compound layer 423 including a luminescent material and acathode 424 made of MgAg, LiF, or the like. The partition walls 420 and421 are provided to cover the end portion of the anode 422, therebypreventing shorts between the cathode and the anode.

It does not matter whether the organic compound layer is made of a lowmolecular material or a high molecular material. A vapor depositionmethod is used in the case of the low molecular material, while a spincoat method, a printing method, or an ink jet method is used in the caseof the high molecular material.

A well-known high molecular material is a π-conjugated polymer material.The typical examples thereof are crystalline semiconductor filmp-phenylene vinylene (PPV) derivatives, poly vinyl carbazole (PVK)derivatives, and polyfluorene derivatives. The organic compound layermade of such a material may be used alone or laminated with other layersto form a laminated structure, although a higher luminous efficiency isobtained in the latter case. Generally, the laminated structure isformed by stacking an anode, a hole injecting layer, a hole transportinglayer, a light-emitting layer, and an electron transporting layer inthis order. However, the laminated structure may be formed by stackingan anode, a hole transporting layer, a light-emitting layer, an electrontransporting layer or a hole injecting layer, a hole transporting layer,a light-emitting layer, an electron transporting layer, and an electroninjecting layer in this order. The present invention can be made withany of well-known laminated constructions. Also, the organic compoundlayer may be doped with a fluorescent coloring agent.

Typical materials are, for instance, disclosed in U.S. Pat. No.4,356,429, U.S. Pat. No. 4,539,507, U.S. Pat. No. 4,720,432, U.S. Pat.No. 4,769,292, U.S. Pat. No. 4,885,211, U.S. Pat. No. 4,950,950, U.S.Pat. No. 5,059,861, U.S. Pat. No. 5,047,687, U.S. Pat. No. 5,073,446,U.S. Pat. No. 5,059,862, U.S. Pat. No. 5,061,617, U.S. Pat. No.5,151,629, U.S. Pat. No. 5,294,369, U.S. Pat. No. 5,294,870, JapanesePatent Application Laid-open No. Hei 10-189525, Japanese PatentApplication Laid-open No. Hei 8-241048, and Japanese Patent ApplicationLaid-open No. Hei 8-78159.

It should be noted here that there are four major methods of displayingcolor images. With the first method, three types of light-emittingelements each corresponding to one of R (red), G (green), and B (blue)are formed. With the second method, a light-emitting element that emitswhite light is combined with a color filter. With the third method, alight-emitting element that emits blue or cyan light is combined with afluorescent member (a fluorescent color changing layer: CCM). With thefourth method, light-emitting elements each corresponding to one of R(red), G (green), and B (blue) are stacked using a transparent electrodeas a cathode (an opposing electrode).

In more detail, an organic compound layer that emits red light is madeof cyanopolyphenylene, an organic compound layer that emits green lightis made of polyphenylenevinylene, and an organic compound layer thatemits blue light is made of polyphenylenevinylene or polyalkylphenylene.Each organic compound layer is 30 to 150 nm in thickness.

Organic EL materials that can be used as a light-emitting layer aregiven above, although the present invention is not limited to them. Anyof available combinations of materials of a light-emitting layer, acharge transporting layer, and a charge injecting layer may be freelyselected. The organic compound layer in this embodiment has aconstruction where a light-emitting element is combined with a holeinjecting layer made of PEDOT (polythiophene) or PAni (polyaniline).

The cathode 424 placed on the organic compound layer 423 is made of amaterial including magnesium (Mg), lithium (Li), or calcium (Ca) eachhaving a low work function. It is preferable that an MgAg electrode(Mg:Ag=10:1) is used as the cathode 424. An MGAgAl electrode, LiAlelectrode, and LiFAl electrode may also be used as the cathode 424.

It is preferred to successively form the organic compound layer 423 andthe cathode 424 without leaving them in the air. This is because thecondition of the interface between the cathode 424 and the organiccompound layer 423 greatly effects the luminous efficiency of thelight-emitting element. Note that in this specification, alight-emitting element means a light-emitting element composed of ananode (pixel electrode), an organic compound layer, and a cathode.

One laminated structure including the organic compound layer 423 and thecathode 424 is required to be formed for each picture element, but theorganic compound layer 423 is extremely vulnerable to moisture.Therefore, an ordinary photolithograph technique cannot be used to formthe laminated structure. Also, the cathode 424 made of an alkaline metalis easily oxidized. As a result, it is preferred to selectively form thelamination member with a vapor phase method, such as a vacuum depositionmethod, a sputtering method, or a plasma CVD method, using a physicalmask, such as a metal mask. Note that it is possible to selectively formthe organic compound layer with another method, such as an ink-jetmethod or a screen printing method, although it is currently impossibleto successively form cathodes with these methods. As a result, it ispreferable to use the vapor phase method.

Also, a protecting electrode for protecting the cathode 424 from theoutside moisture and the like may be stacked on the cathode 424. It ispreferable that the protecting electrode is made of a low resistantmaterial including aluminum (Al), copper (Cu), or silver (Ag).Alternatively the protecting electrode may be a transparent electrode.In this case, light is emitted in the direction of the arrow shown inFIG. 4 (the light emission in this direction is hereinafter referred toas a “top surface emission”, for ease of explanation). In this case, bymixing a black pigment into the organic resin interlayer insulating film419, no polarizing plate is required to form a black screen during anon-light-emission period. This protecting electrode is also expected toachieve a heat dissipation effect that lowers the temperature of theorganic compound layer. It is also effective to successively form theorganic compound layer 423, the cathode 424, and the protectingelectrode without leaving them in the air.

In FIG. 47 the switching TFT 454 has a multi-gate construction and thecurrent control TFT 455 is provided with an LDD overlapping the gateelectrode. A TFT produced using a polysilicon operates at high speed andtherefore degradation, such as hot carrier injection, tends to occur forthe TFT. Therefore, TFTs are formed to have different constructionsaccording to their functions and are provided in a pixel portion (in thecase of FIG. 2, the switching TFT whose OFF current is sufficientlyreduced is combined with the current control TFT that is resistant tohot carrier injection), which is highly effective in producing a displaydevice that achieves high reliability and superior image display (highoperation performance).

FIG. 6 shows the external appearance of such a display device. Thedirection in which an image is displayed depends on the construction ofthe light-emitting element, although light is emitted upward to displayimage in this drawing. In FIG. 6, an element substrate 601, on whichdriving circuit portions 604 and 605 and a pixel portion 603 have beenformed using TFTs, and a seating substrate 602 are laminated using asealing member 610. One end of the element substrate 601 is providedwith an input terminal 608 via which an FPC is connected to the displaydevice. The input terminal 608 includes a plurality of terminals thatreceive an image data signal, various timing signals, and electricityfrom an external circuit. Here, the interval between the terminals isset at 500 μm. The input terminal 608 is connected to the drivingcircuit portion via wiring 609. Here, an IC ship 607 on which a CPU anda memory have been formed may be mounted on the element substrate 601using a COG (Chip on Glass) method or the like, as necessary.

A DLC film 611 is formed in end portions to prevent moisture and oxygenfrom entering through sealed portions and being degraded inlight-emitting elements. In the case where the element substrate 601 andthe sealing substrate 602 are made of an organic resin material, the DLCfilm may be formed to coat the entire surface of the display device,except for an input terminal, as described by referring to FIG. 1C. Inthis case, the input terminal is covered with a masking tape or a shadowmask prior to the formation of the DLC film.

As shown in FIG. 7, the input terminal is formed by stacking an ITO 706formed as an anode on wiring 705 made of titanium (Ti) and aluminum(Al). Incidentally, FIG. 8 is a cross-sectional view of the inputterminal taken along the line C-C′. An element substrate 701 and a coversubstrate 702 are laminated using a sealing member 703 and a DLC film704 is formed to cover the sealing member 703 and the end portions ofthe element substrate 701 and the cover substrate 702. In the drivingcircuit portion, an organic compound layer 707 and a cathode 708 areformed on a partition wall 709 and a contact region 710 is formed toestablish the contact between the cathode 708 and the wiring, as shownin FIG. 7.

By forming DLC films on a display device that uses an organic resinsubstrate, the degradation of light-emitting elements is prevented andthe stability of the display device is ensured for the long term. Thedisplay device using the organic resin substrate is in particularsuitable as a display device for a portable device. If the portabledevice is used outdoors, however, it is required to increase thereliability of the display device in consideration of the exposure tothe direct sunlight, wind, and rain. The DLC films also satisfy thisrequirement for increasing the reliability of the display device.

Embodiment 2

In this embodiment, the degradation of a light-emitting element isprevented using a means for sealing a dryer agent, such as barium oxide,in gaps of a light-emitting device or a space in which thelight-emitting element is seated. In FIGS. 1A to 1D, a dryer agent isprovided on a driving circuit or in areas in which a sealing member hasbeen formed. In the present embodiment, a dryer agent is provided in adifferent manner, as shown in FIGS. 9A to 9C. As can be seen from thesedrawings, a dryer agent is arranged in partition walls that are providedto separate adjacent picture elements in a pixel portion. FIGS. 9A to 9Care each a cross-sectional view taken alone the line B-B′ in FIG. 5. Forease of explanation, the same reference numerals as in FIGS. 4, 5A, and5B are used in FIGS. 9A to 9C.

FIG. 9A shows an example where a dryer agent 480 is dispersed in thepartition wall 421. The partition wall 421 is made of a thermosetting orphotosensitive organic resin material. The dryer agent is dispersed inthe organic resin material prior to the polymerization of the organicresin material, and then the organic resin material including the dryeragent is applied as it is to form the partition wall 421.

FIG. 9B shows an example where a dryer agent 481 is formed on an organicresin insulating film 419. In this case, the dryer agent is formed at apredetermined position to have a predetermined pattern using a vacuumdeposition method or a printing method. Then, the partition wall 421 isformed on the dryer agent 481.

FIG. 9C shows an example where a dryer agent 432 is formed on thepartition wall 421. In this case, the dryer agent 482 is formed using avacuum deposition method or a printing method, similarly to the caseshown in FIG. 9B.

FIGS. 9A to 9C show examples of the formation of the dryer agent, andthese examples may be combined with each other as appropriate. Also, theconstructions of the present embodiment may be combined with theconstruction shown in FIG. 1. If the stated formations of the dryeragent are applied to the display device of Embodiment 1, a displaydevice with high reliability is realized by the dryer agent combinedwith the gas barrier property of the DLC films.

Embodiment 3

FIG. 10 shows an example of a display device that uses an invertedstagger type TFT. A substrate 501 and a light-emitting element 556 usedin this embodiment are the same as those of Embodiment 1 and thereforeare not described here.

The inverted stagger type TFT is formed by stacking the substrate 501,gate electrodes 508 to 511, gate insulating films 507, and semiconductorfilms 503 to 506 in this order. In FIG. 10, an N-channel type TFT 552and a P-channel type TFT 553 are formed in a driving circuit portion550. Also, a switching TFT 554, a current control TFT 555, and alight-emitting element 556 are formed in a pixel portion 551. Aninterlayer insulating film is composed of an inorganic insulating film518 made of silicon nitride or silicon oxynitride and an organic resinfilm 519 made of acrylic or polyimide.

The driving circuit portion 550 includes a gate-signal-side drivingcircuit and a data-signal-side driving circuit having different circuitconstructions, although the circuit constructions are not describedhere. The N-channel type TFT 552 and the P-channel type TFT 553 areconnected to wiring 512 and 513 and form a shift resister, a latchcircuit, and a buffer circuit.

In the pixel portion 551, data wiring 514 is connected to the sourceside of the switching TFT 554 and drain-side wiring 515 is connected toa gate electrode 511 of the current control TFT 555. Also, the source ofthe current control TFT 555 is connected to a power supplying wiring 517so as to connect a drain-side electrode 516 to an anode of thelight-emitting element.

Partition walls 520 and 521 are formed using an organic resin, such asacrylic or polyimide, or preferably a photosensitive organic resin tocover the wiring. The light-emitting element 556 is composed of an anode522 made of ITO (indium tin oxide), an organic compound layer 523produced using an organic EL material, and a cathode 524 made of MgAg,LiF or the like. The partition walls 520 and 521 are provided to coverthe end portion of the anode 522, thereby preventing shorts between thecathode and the anode.

Components other than the TFTs, such as the pixel portion, of thedisplay device have the same constructions as in Embodiment 1. It isadvantageous to use the inverted stagger type TFT produced usingpolysilicon because the manufacturing line for amorphous silicon TFTs(usually formed as inverted stagger type TFTs) can be used as it is.Needless to say, a laser anneal technique using an eximer laser makes itpossible to produce polysilicon TFTs at a processing temperature of 300°C. or below.

Embodiment 4

In this embodiment, an example of construction of an electronic deviceusing the display device of Embodiment 1 is described with reference toFIG. 11. A display device 900 in FIG. 11 includes a pixel portion 921,which is composed of picture elements 920 formed by TFTs on a substrate,and a data-signal-side driving circuit 915 and a gate-signal-sidedriving circuit 914 that are used to drive the pixel portion. In theexample shown in FIG. 11, the data-signal-side driving circuit 915 usesa digital driving method and includes a shift register 916, latchcircuits 917 and 918, and a buffer circuit 919. Also, thegate-signal-side driving circuit 914 includes various components, suchas a shift register and a buffer (not shown).

In the case of VGA, the pixel portion 921 includes 640 picture elementswide by 480 picture elements high. Also, as described by referring toFIGS. 4, 5A, and 5B, a switching TFT and a current control TFT arearranged for each picture element. The light-emitting element operatesas follows. When gate wiring is selected, the gate of the switching TFTopens, data signal on source wiring is accumulated in a capacitor, andthe gate of the current control TFT opens. That is, data signal inputtedfrom the source wiring causes the flow of current into the currentcontrol TFT and the light-emitting element emits light.

The system block diagram shown in FIG. 11 relates to the application ofthe display device of Embodiment 1 to a portable information terminal,such as a PDA. The display device of Embodiment 1 includes a pixelportion 921, a gate-signal-side driving circuit 914, and adata-signal-side driving circuit 915.

An external circuit connected to the display device includes a powercircuit 901 composed of a stabilized power source and a high-speed andhigh-precision operational amplifier, an external interface port 902provided with a USB terminal or the like, a CPU 903, an input meanscomposed of a pen input tablet 910 and detection circuit 911, a clocksignal oscillator 912, and a control circuit 913.

The CPU 903 includes, an image signal processing circuit 904 and atablet interface 905 for receiving signals from the pen input tablet910, and is connected to a VRAM 906, a DRAM 907, a flash memory 908, anda memory card 909. Information processed in the CPU 903 is sent as animage signal (data signal) from the image signal processing circuit 904to the control circuit 913. The control circuit 913 has a function ofconverting the image signal and a clock signal to signals which can beused corresponding to the data-signal-side driving circuit 915 and thegate-signal-side driving circuit 914, respectively.

In more detail, the control circuit 913 has a function of dividing theimage signal into a plurality of pieces of data corresponding torespective picture elements. The control circuit 913 also has a functionof converting a horizontal synchronizing signal and a verticalsynchronizing signal inputted from the outside into two signals: a startsignal used by the driving circuit, and a timing control signal requiredto convert the current generated by an internal power circuit into analternating current.

It is desired that a portable information terminal, such as a PDA, canbe used outdoors (in a train, for instance) for a long time using arechargeable battery as a power supply (that is, without connecting theterminal to an AC outlet). Such an electronic device is also required tobe easily portable and thus the weight and size thereof need to bereduced. The battery occupying the majority of weight of the electronicdevice increases in weight in accordance with the increase in batterycapacity. Accordingly, various measures based on software techniquesneed to be used to reduce the power consumption of the electronicdevice. For instance, the time period in which a backlight is turned onis controlled or a standby mode is used.

In the case of the electronic device of the present embodiment, if noinput signal is inputted from the pen input tablet 910 into the tabletinterface 905 of the CPU 903 for a predetermined time period, theelectronic device is placed in a standby mode and the componentsenclosed with dotted lines in FIG. 11 stop their operations insynchronization with each other. Also, the display device reduces thestrength of light emitted by the light-emitting element or stops theimage displaying operation. Alternatively, memories corresponding torespective picture elements may be used to change the electronic deviceinto a still image displaying mode. With these measures, the powerconsumption of the electronic device is reduced.

Also, a still image may be displayed by stopping the operations of theimage signal processing circuit 904 of the CPU 903 and the VRAM 906 toreduce the power consumption. In FIG. 11, the components that continueto operate even in the still image displaying mode are indicated usingdotted lines. Also, as shown in FIG. 6, the control circuit 913 may bemounted on the element substrate using an IC chip with a COG method, orintegrally formed in the display device.

The display device using the organic resin substrate of the presentinvention contributes to the weight reduction of an electronic device.If a display device whose size is five inches or the like is used for anelectronic device, the weight of the electronic device becomes around 60g with a glass substrate. However, with a display device using theorganic resin substrate of the present invention, the weight of theelectronic device is reduced to 10 g or less. Further, because DLC filmscoat the surface of the display device, the surface increases inhardness and becomes resistant to scratches or the like. As a result,the beautiful condition of the display screen is continued. As describedabove, the present invention achieves a superior effect for anelectronic device, such as a portable information terminal.

Embodiment 5

In this embodiment, a method of forming a cathode of a light-emittingelement is described with reference to FIGS. 16A to 16C. In thesedrawings, an insulating film 1601, an anode 1602 formed as a firstelectrode, an organic compound layer 1603, a cathode 1604 formed as asecond electrode, and a DLC film 1605 are stacked in this order.

First, the description is given of FIG. 16A below. In this drawing, asilicon oxide film is used as the insulating film 1601, a conductiveoxide film (thickness=120 nm) formed by adding gallium oxide to zincoxide is used as the anode 1602, and a lamination film composed ofcopper-phthalocyanine (a hole injecting layer) with a thickness of 20 nmand Alq₃ (quinolilato-aluminum complex: light-emitting layer) with athickness of 50 nm is used as the organic compound layer 1603. Thecathode 1604 has a laminated construction where a transparent electrode1604 b is stacked on a translucent electrode 1604 a formed using anultra-thin metal film. For instance, the translucent electrode 1604 a isformed using an MgAg film with a thickness of 20 nm (alloy film formedby evaporating magnesium and silver) and the transparent electrode 1604b is formed using a conductive oxide film (thickness=200 nm) formed byadding gallium oxide to zinc oxide. A protecting film 1605 is formedusing a DLC film.

Also, in FIG. 16B, the insulating film 1601, the anode 1602, the organiccompound layer 1603, and an electron injecting layer 1606 that is a LiFfilm are stacked in this order. The cathode 1604 that is a conductiveoxide film (thickness=200 nm) formed by adding gallium oxide to zincoxide and a protecting film 1605 formed using a DLC film are stacked onthe electron injecting layer 1606.

In FIG. 16C, the insulating film 1601, the anode 1602, and the organiccompound layer 1603 are stacked in this order. Then an LiF film 1606 isstacked on the organic compound layer 1603 as an electron injectinglayer, and the cathode 1604 is stacked on the film 1606. The cathode1604 is composed of the translucent electrode 1604 a that is an MgAgfilm with a thickness of 50 nm or less (preferably, 20 nm) (alloy filmformed by evaporating magnesium and silver) and the transparentelectrode 1604 b that is a conductive oxide film (thickness=200 nm)formed by adding gallium oxide to zinc oxide. The protecting film 1605that is formed using a DLC film is stacked on the cathode 1604.

After a light-emitting element is formed to have any one of theconstructions described above, the light-emitting element is sealed andDLC films are formed at end portions with any one of the aforementionedmethods. In this manner, the degradation due to oxygen and moisture isprevented.

Embodiment 6

In this embodiment, the cathode of a light-emitting element is formedwith a method differing from that of Embodiment 1. Here, the method offorming a cathode is below described with reference to FIGS. 17A and17B. In FIG. 17A, a cathode 1702 made of an alkaline metal (Li or Mg,for instance) with a low work function is formed on an insulating film1701. Then, an organic compound layer 1703, an anode 1704, and aprotecting layer 1705 (a DLC film) are formed on the cathode 1702.

In FIG. 17B, a transparent electrode 1702 a that is a transparentconductive film ITO and a translucent electrode 1702 b that is anultra-thin (thickness=50 nm or less) metal film (Al—Li alloy film or Mgalloy film, for instance) are stacked in this order on the insulatingfilm 1701 to form the cathode 1702. Then, the organic compound layer1703, the anode 1704, and the protecting film 1705 that is a DLC filmare formed on the cathode 1702.

Embodiment 7

In this embodiment, the organic compound layer is described in moredetail. Accordingly, it is possible to combine the present embodimentwith any construction of the embodiment modes and Embodiments 1 to 6.Note that in this embodiment, an anode 1801 that is a first electrode isformed using a conductive oxide film. Also, a cathode that is a secondelectrode is formed using a conductive film to have any of constructionsdescribed with reference to FIGS. 18A to 18D.

FIG. 18A shows a construction where an anode 1801, a hole injectinglayer 1802, a hole transporting layer 1803, a light-emitting layer 1804,an electron transporting layer 1805, an electron injecting layer 1806,and a cathode 1807 are formed and stacked in this order. FIG. 18B showsa construction where the anode 1801, the hole injecting layer 1802, thelight-emitting layer. 1804, the electron transporting layer 1805, theelectron injecting layer 1806, and the cathode 1807 are formed andstacked in this order. FIG. 18C shows a construction where the anode1801, the hole injecting layer 1802, the light-emitting layer 1804, theelectron injecting layer 1806, and the cathode 1807 are formed andstacked in this order. FIG. 18D shows a construction where the anode1801, the hole injecting layer 1802, the hole transporting layer 1803,the light-emitting layer 1804, and the cathode 1807 are formed andstacked in this order.

These are just a few examples of the construction of the organiccompound layer and therefore there are various different constructionsthat can be used for the present invention. It is possible to use thestated constructions of the organic compound layer in combination withEmbodiments 1 to 6.

Embodiment 8

In this embodiment, in addition to DLC films formed at end portions of alight-emitting device, a dryer agent is provided in a light-emittingelement to prevent the degradation due to oxygen and moisture. Thisconstruction is described with reference to FIGS. 19A and 19B. Referencenumeral 1901 represents a glass substrate that is a first substrate, anda base insulating film 1902 is formed on the first substrate 1901. Anamorphous silicon layer is formed on the base insulating film 1902 andis crystallized using a well-known technique to produce a crystallinesilicon film, then the crystalline silicon film is processed to have anisland-like pattern, thereby forming an active layer 1904 of each TFT.

A gate insulating film (not shown), gate electrodes 1905, interlayerinsulating films 1906, and pixel electrodes (first electrodes) 1907 madeof an alkaline metal or an alkaline earth metal with a low work functionare formed on the active layer. An organic compound layer 1908 is formedon the pixel electrodes 1907, and an anode (second electrode) 1909 isformed on the organic compound layer 1908 using a conductive oxide film(ITO film, in this embodiment) made of a compound of an indium oxide anda tin oxide.

A partition wall 1910 is formed under the organic compound layer tocover each TFT. Here, if the partition wall is made of a materialproduced by mixing a dryer agent with a resin, moisture existing underthe protecting layer 1911 is absorbed by the partition wall and thedegradation of the light-emitting element is prevented.

FIG. 19B shows another example where a resin (hereinafter, a dryeragent) 1912 mixed with a dryer agent is provided on the protective layer1911 in the area of a driving circuit. This dryer agent 1912 alsofunctions as a spacer. Note that the arrangement positions of the dryeragent 1912 may be freely determined so long as the agent is not arrangedon input wiring or in areas in which pixel electrodes emit light. Also,the dryer agent 1912 may be provided by combining the stated arrangementmethods. Further the present embodiment may be combined with any of theconstructions described in Embodiments 1 to 7.

Embodiment 9

In this embodiment, a first substrate (such as a glass substrate) 2001is laminated with a third substrate (a film-like substrate, such as aplastic film or an ultra-thin stainless substrate) 2004 on which alight-emitting element is to be formed. After the formation of thelight-emitting element, the third substrate 7004 is laminated with asecond substrate 2003. Then the glass substrate 2001 is peeled off usinga laser or an agent and a film-like substrate is instead laminated. Thisprocessing is described in detail below with reference to FIGS. 20A and20B.

After the light-emitting element formed on the third substrate 2004 issealed with the second substrate 2003, a laser light is applied onto theundersurface of the glass substrate 2001 to evaporate a bonding layer2002 (such as polyimide, polyamide, polyimideamide, an urethane resin, aphoto-curing resin, a thermosetting resin, a polychlorinated vinylresin, an epoxy resin, an acrylic adhesive, and a gum adhesive). In thismanner, the glass substrate 2001 is peeled off. In this embodiment, alinear beam is formed using the second harmonic (wavelength=532 nm) of aYAG laser and is irradiated onto the bonding layer 2002 through theglass substrate 2001. As a result, the bonding layer 2002 is evaporatedand the glass substrate 2001 is peeled off.

After this, a plastic film substrate or a thin metal substrate islaminated instead of the peeled glass substrate. This realizes aflexible light-emitting device whose weight and thickness are bothreduced. Note that it does not matter whether the bonding layer 2002 islaminated with the first substrate 2001 and then the third substrate2004 or is laminated with the third substrate 2004 and then the firstsubstrate 2001. The present embodiment may be combined with any of theembodiment modes and Embodiments 1 to 8.

Embodiment 10

In this embodiment, an organic compound layer is produced by combiningan organic compound (hereinafter, a singlet compound) that emits lightby a singlet exciton (singlet) and an organic compound (hereinafter, atriplet compound) that emits light by a triplet exciton (triplet). Here,the singlet compound means a compound that emits light only via asinglet excited state and the triplet compound means a compound thatemits light via a triplet excited state.

Typical organic compounds that can be used as the triplet compound aredescribed in the following theses.

-   (1) T. Tsutsui, C. Adachi, S. Saito, Photochemical Processes in    Organized Molecular Systems, ed. K. Honda, (Elsevier Sci. Pub.,    Tokyo, 1991) p. 437-   (2) M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S.    Sibley, M. E. Thompson. S. R. Rorrest, Nature 395 (1998) p. 151    *This thesis discloses an organic compound expressed by the    following formula.-   (3) M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R.    Forrest, Appl. Phys. Lett., 75 (1999) p. 4-   (4) T. Tsutsui, M.-J. Yang, M. Yahiro, K. Nalamura, T. Watanabe, T.    Tsuji, Y. Fukuda, T. Wakimoto, S. Mayaguchi, Jpn. Appl. Phys., 38    (12B) (1999) L1502

In addition to the luminescent materials described in the above theses,it is thought that luminescent materials (in more detail, metalcomplexes and organic compounds) expressed by the following molecularformulas may also be used.

(“Et” indicates ethyl group. “M” indicates an element belonging toVIII-X groups in periodic table.)

(“M” indicates an element belonging to VIII-X groups in periodic table.)

In the above molecular formulas, V is an element belonging to Group 8,9, or 10 of the periodic table. In the above theses, platinum andiridium are used. However, the inventors of the present inventionconsider that it is preferable to use nickel, cobalt, or palladiumbecause these materials are inexpensive compared with platinum andiridium and therefore suitable for reducing the cost of fabricatinglight-emitting devices. It is thought that nickel is in particularpreferable because nickel complexes are easy to form and thus theproductivity is increased.

The triplet compound has a higher luminous efficiency than the singletcompound and it is possible to reduce an operating voltage (voltagerequired to have a light-emitting element emit light) without reducingthe amount of emitted light and brightness. This embodiment is madeusing this feature.

If a low-molecular organic compound is used as a light-emitting layer,the life span of a light-emitting layer that emits red light is shorterthan those of light-emitting layers that emit other colored lights underpresent circumstances. This is because the luminous efficiency of thered-light-emitting layer is lower than those of theother-colored-light-emitting layers and the operating voltage thereof isrequired to be increased to obtain the same brightness as those of theother-colored-light-emitting layers. This promotes the degradation ofthe red-light-emitting layer.

In this embodiment, however, a triplet compound having a high luminousefficiency is used as the red-light-emitting layer, so that theoperating voltage thereof does not be required to be increased to obtainthe same brightness as those of the light-emitting layers that emitgreen and blue lights. Accordingly, a situation is avoided where thedegradation of the red-light-emitting-element is extremely accelerated.As a result, it becomes possible to display color images without causingproblems, such as color deviations. The reduced operating voltage isalso preferable because it becomes unnecessary for transistors to havehigh withstand voltages.

It should be noted here that the triplet compound is used as thelight-emitting layer that emits red light in this embodiment, althoughthe triplet compound may also be used as the light-emitting layer thatemits green light or the light-emitting layer that emits blue light.

In the case of RGB color display, three types of light-emitting elementsthat respectively emit red light, green light, and blue light need to beprovided in a pixel portion. In this case, it is possible to use thetriplet compound for the light-emitting element that emits red light anduse the singlet compound for other light-emitting elements.

By selectively using the triplet compound and the singlet compound inthis manner, it becomes possible to have each light-emitting elementoperate at the same operating voltage (10V or less, preferably 3 to10V). Accordingly, all power sources for the light-emitting device canhave the same voltage (3V or 5V), which allows circuit design to becarried out without difficulty. Note that the construction described inthis embodiment may be combined with any of the constructions ofEmbodiments 1 to 6.

Embodiment 11

A light-emitting device formed by implementing the present invention canbe incorporated to various electric-equipment, and a pixel portion isused as an image display portion. Given as such electronic equipment ofthe present invention are cellular phones, PDAs, electronic books, videocameras, notebook computers, and image play back devices with therecording medium, for example, DVD (digital versatile disc), digitalcameras, and the like. Specific examples of those are shown in FIGS. 12Ato 13D.

FIG. 12A shows a cellular phone, which is composed of a display panel9001, an operation panel 9002, and a connecting portion 9003. Thedisplay panel 9001 is provided with a display device 9004, an audiooutput portion 9005, an antenna 9009, etc. The operation panel 9002 isprovided with operation keys 9006, a power supply switch 9002, an audioinput portion 9008, etc. The present invention is applicable to thedisplay device 9004.

FIG. 12B also shows a cellular phone, which is composed of a main bodyor a housing 9101, a display device 9102, an audio output portion 9103,an audio input portion 9104, and an antenna 9105. The display device9102 can be provided with a touch sensor so as to operate buttons on thedisplay. By using the organic resin substrate of the present invention,the substrate can be bent after the completion of the display device.Therefore, while such characteristics are used, the housing with 3dimensional curing surfaces, which is designed based on the humanengineering can be employed by the display device without difficulty.

FIG. 12C shows a mobile computer, or a portable information terminal,which is composed of a main body 9201, a camera portion 9202, an imagereceiving portion 9203, operation switches 9204, and a display device9105. The present invention can be applied to the display device 9205.In such electronic devices, the display device of 3 to 5 inches isemployed, however, by employing the display device of the presentinvention, the reduction of the weight in the portable informationterminal can be attained.

FIG. 1D shows a portable book, which is composed of a main body 9301,display devices 9303, and a recording medium 9304, an operation switch9305, and an antenna 9306, and which displays the data recorded in MD orDVD and the data received by the antenna. The present invention can beapplied to the display devices 9302. In the portable book, the displaydevice of the 4 to 12 inches is employed. However, by employing thedisplay device of the present invention, the reduction of the weight andthickness in the portable book can be attained.

FIG. 12E shows a video camera, which is composed of a main body 9401, adisplay device 9402, an audio input portion 9403, operation switches9404, a battery 9405, and the like. The present invention can be appliedto the display device 9402.

FIG. 13A shows a personal computer, which is composed of a main body9601, an image input portion 9602, a display device 9603, and a keyboard 9604. The present invention can be applied to the display device9601.

FIG. 13B shows a player employing a recording medium with programsrecorded thereon (hereinafter referred to as recording medium), which iscomposed of a main body 9701, a display device 9702, a speaker portion9703, a recording medium 9704, and an operation switch 9705. The deviceemploys DVD (digital versatile disc), CD, etc. as the recording mediumso that music can be listened, movies can be seen and games and internetcan be done. The present invention can be applied to the display device9702.

FIG. 13C shows a digital camera, which is composed of a main body 9801,a display device 9802, an eyepiece portion 9803, an operation switch9804, and an image receiving portion (not shown). The present inventioncan be applied to the display device 9802.

FIG. 13D also shows a digital camera, which is composed of a main bode9901, a display device 9902, an image receiving portion 9903, anoperation switch 9904, a battery 9905, etc. The present invention can beapplied to the display device 9902. By using the organic resin substrateof the present invention, the substrate can be bent after the completionof the display device. Therefore, while such characteristics are used,the housing with 3 dimensional curing surfaces, which is designed basedon the human engineering can be employed by the display device withoutdifficulty.

The display device of the present invention is employed in the cellularphones in FIGS. 12A and 12B, the mobile computer or the portableinformation terminal in FIG. 12C, the portable book in FIG. 12D, and thepersonal computer in FIG. 13A. The display device can reduce the powerconsumption of the above device by displaying white letters on the blackdisplay in a standby mode.

In the operation of the cellular phones shown in FIGS. 12A and 12B,luminance is lowered when the operation keys are used, and the luminanceis raised after usage of the operation switch, whereby the low powerconsumption can be realized. Further, the luminance of the displaydevice is raised at the receipt of a call, and the luminance is loweredduring a call, whereby the low power consumption can be realized.Besides, in the case where the cellular phone is continuously used, thecellular phone is provided with a function of turning off a display bytime control without resetting, whereby the low power consumption can berealized. Note that the above operations may be conducted by manualcontrol.

FIGS. 21A and 21B show cellular phones. Reference numeral 2701 denotes adisplay panel, and reference numeral 2702 denotes an operation panel.The display panel 2701 and the operation panel 2702 are connected in theconnection portion 2703. The cellular phone has a display portion 2704,an audio output portion 2705, operation keys 2706, a power supply switch2707, and an audio input portion 2708. The present invention can beapplied to the display portion 2704. FIGS. 21A and 21B show thelengthwise cellular phone and the widthwise cellular phone,respectively.

FIG. 21C shows a car audio system, which is composed of a main body2801, a display portion 2802, and operation switches 2803 and 2804. Thelight-emitting device of the present invention can be applied to thedisplay portion 2802. In this embodiment the car audio system for beingmounted in a car is shown. However, it can be applied to the standstillcar audio. The display portion 2804 can reduce the power consumption bydisplaying white letters in the black display.

Further, it is effective to incorporate an optical sensor and to providea function of modulating emission luminance in accordance withbrightness in a usage environment by providing means for detecting thebrightness in the usage environment. A user can recognize image orcharacter information without problems if brightness of 100 to 150 incontrast ratio in comparison with the brightness of the usageenvironment is secured. That is, it is possible that the luminance of animage is raised in the bright usage environment to make the image easyto see while the luminance of an image is suppressed in the dark usageenvironment to thereby suppress the power consumption.

Although it is not shown here, the present invention can be applied tothe display device which is employed in a navigation system, arefrigerator, a washing machine, a micro-wave oven, a telephone, a faxmachine, etc. As described above, the applicable range of the presentinvention is so wide that the present invention can be applied tovarious products.

According to the present invention described above, in a display devicethat uses an organic resin substrate, DLC films are formed on the outersurfaces of a sealing member and an outer surface or end portions of theorganic resin substrate. This construction improves the gas barrierproperty of the display device and prevents the degradation oflight-emitting elements. Also, if a DLC film is formed on a lightincident surface, ultraviolet rays are blocked, the light chemicalreaction of the organic resin substrate is suppressed and thedegradation of the organic resin substrate is prevented.

Such a display device realizes an electronic device whose weight isreduced and shock resistance is improved. Also, the surface on which aDLC film has been formed is hardened, so that the surface of an organicresin substrate becomes resistant to flaws. As a result, a high-qualitydisplay screen is achieved and remains clear for a long time.

By forming a DLC film to cover end portions of substrates, from enteringoxygen and moisture through between the substrates is prevented. Thisachieves the prolonged life spans of light-emitting elements and alight-emitting device. Also, by providing a DLC film to cover the entiresurface except for an area in which light emission is performed, itbecomes unnecessary to strictly control the formation of the DLC film.Further, by forming an interlayer insulating film using a black resin,the reflection of light by the first substrate is prevented. As aresult, a problem in that outside scenes, such as the face of anobserver, is reflected by a light-emitting device is solved withoutusing an expensive circular polarizing film.

1. A cellular phone comprising: a bent housing; and a display deviceincorporated into the bent housing, wherein the display device includesa light-emitting element formed over a substrate, and wherein thedisplay device has a bent display surface in a same direction as thebent housing.
 2. A cellular phone according to claim 1, wherein thesubstrate comprises one selected from the group consisting of polyimide,polyethylene terephthalate, polyethylene naphthalate, polyether sulfone,and aramid.
 3. A cellular phone according to claim 1, wherein thesubstrate has a thickness of 30 to 120 μm.
 4. A cellular phone accordingto claim 1, wherein a touch sensor is provided with the display device.5. A cellular phone comprising: a bent housing; and a display deviceincorporated into the bent housing, wherein the display device includesa light-emitting element formed over a flexible substrate, and whereinthe display device has a bent display surface in a same direction as thebent housing.
 6. A cellular phone according to claim 5, wherein theflexible substrate comprises one selected from the group consisting ofpolyimide, polyethylene terephthalate, polyethylene naphthalate,polyether sulfone, and aramid.
 7. A cellular phone according to claim 5,wherein the flexible substrate has a thickness of 30 to 120 μm.
 8. Acellular phone according to claim 5, wherein a touch sensor is providedwith the display device.
 9. A cellular phone comprising: a bent housing;and a display device incorporated into the bent housing, wherein thedisplay device includes a light-emitting element formed over asubstrate, and wherein the display device has a recessed displaysurface.
 10. A cellular phone according to claim 9, wherein thesubstrate comprises one selected from the group consisting of polyimide,polyethylene terephthalate, polyethylene naphthalate, polyether sulfone,and aramid.
 11. A cellular phone according to claim 9, wherein thesubstrate has a thickness of 30 to 120 μm.
 12. A cellular phoneaccording to claim 9, wherein a touch sensor is provided with thedisplay device.
 13. A cellular phone comprising: a bent housing; and adisplay device incorporated into the bent housing, wherein the displaydevice includes a light-emitting element formed over a flexiblesubstrate, and wherein the display device has a recessed displaysurface.
 14. A cellular phone according to claim 13, wherein theflexible substrate comprises one selected from the group consisting ofpolyimide, polyethylene terephthalate, polyethylene naphthalate,polyether sulfone, and aramid.
 15. A cellular phone according to claim13, wherein the flexible substrate has a thickness of 30 to 120 μm. 16.A cellular phone according to claim 13, wherein a touch sensor isprovided with the display device.